Embodiments described herein relate generally to the preparation of electrode cells for use in electrochemical devices and more particularly to systems and methods of using a semi-solid electrode cell in a battery module.
Conventional battery systems store electrochemical energy by separating an ion source and ion sink at differing ion electrochemical potential. A difference in electrochemical potential produces a voltage difference between the positive and negative electrodes, which produces an electric current if the electrodes are connected by a conductive element. In a convention battery system, negative electrodes and positive electrodes are connected via a parallel configuration of two conductive elements. The external elements exclusively conduct electrons, however, the internal elements, being separated by a separator and electrolyte, exclusively conduct ions. The external and internal flow streams supply ions and electrons at the same rate, as a charge imbalance cannot be sustained between the negative electrode and positive electrode. The produced electric current can be used to drive an external device. A rechargeable battery can be recharged by application of an opposing voltage difference that drives electric and ionic current in an opposite direction as that of a discharging battery. Accordingly, active material of a rechargeable battery requires the ability to accept and provide ions. Increased electrochemical potentials produce larger voltage differences between the cathode and anode of a battery, which increases the electrochemically stored energy per unit mass of the battery. For high-power batteries, the ionic sources and sinks are connected to a separator by an element with large ionic conductivity, and to the current collectors with high electric conductivity elements.
Typical battery manufacturing involves numerous complex and costly processes carried out in series, each of which is subject to yield losses, incurs capital costs for equipment, and includes operating expenses for energy consumption and consumable materials. The process first involves making separate anodic and cathodic mixtures that are typically mixtures of electrochemically active ion storage compounds, electronically conductive additives, and polymer binders. The mixtures are coated onto the surfaces of flexible metal foils and subsequently compressed under high pressure to increase density and control thickness. These compressed electrode/foil composites are then slitted into sizes and/or shapes that are appropriate for the particular form factor of the manufactured battery. The slitted electrode composites are typically co-wound or co-stacked with intervening ionically-conductive/electronically-insulating separator membranes to construct battery windings, i.e. “jelly rolls” or “stacks,” which are then packaged in metal cans, flexible polymer pouches, etc. The resulting cells can be infiltrated with liquid electrolyte that need be introduced in a carefully controlled environment.
The stored energy or charge capacity of a manufactured battery is related to the inherent charge capacity of the active materials (mAh/g), the volume of the electrodes (cm3), the product of the thickness, area, and number of layers, and the loading of active material in the electrode media (e.g., grams of active material/cubic centimeters of electrode media. Therefore, to enhance commercial appeal (e.g., increased energy density and decreased cost), it is generally desirable to increase areal charge capacity (mAh/cm2) of the electrodes that are to be disposed in a given battery form factor, which depends on electrode thickness and active material loading. Moreover, it is desirable to increase electrical conduction between the current collector and the electrode material. For example, it can be desirable to increase the surface area of the current collector that is in physical and/or electrical connection with a semi-solid electrode material.
Binder-free electrode formulations can exhibit a wide range of rheological characteristics depending on their constituent types (e.g., composition), component concentrations, manner of preparation, and electrochemical and/or temporal history. Furthermore, in gravitational fields and/or when subjected to shear gradients during mixing or flow, particle segregation can occur, depending on relative densities, particles shapes and sizes, and carrier fluid properties (e.g., viscosity, and flow geometry) that can lead to non-uniformity of the electrode formulations. Thus, a need exists for an electrode that does not substantially include a binder agent and for a manufacturing process that addresses the rheological characteristics of a binder-free electrode.